Update README.md: warning notation

Co-authored-by: Sebastian Romero <[email protected]>

Author: leonardocavagnis

README.md

@@ -1,9 +1,8 @@
 # [Deprecated] Portenta Machine Control Library for Arduino
 
-> ⚠️ **Warning**: This library is deprecated and no longer actively maintained.
-
+> [!WARNING]
+> This library is deprecated and no longer actively maintained.
 > We recommend transitioning to the [Arduino_PortentaMachineControl](https://github.com/arduino-libraries/Arduino_PortentaMachineControl) library for ongoing support, new features and contributions.
-
 > Please note that the [examples](./examples/) provided with this library are not compatible with the new library.
 
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